The present invention relates to a method of force-transmitting clamping of a tool, in particular with a shaft in an opening of a tool receptacle by shrinking including heating and cooling, wherein the axial insertion depth of the shaft in the opening is provided by an adjustment.
In this method the heating is preferably performed inductively. In the method with thermal clamping of tools, a high-precise mounting of the tools, for example drills, mills and the like is obtained. The tool receptacle is heated at least in the region of a sleeve part which contains the opening so that the opening is increased. The tool is inserted with its shaft in the thusly increased opening. During subsequent cooling the shaft of the tool is forced-transmittingly held in the opening of the tool receptacle which is shrunk by cooling. The diameter of the opening of the tool receptacle and the shaft of the tool are selected so that during cooling a force-transmitting (force-locking) and non rotatable connection is produced, such that during fast rotation it is not released under the action of centrifugal forces. In order to remove the tool, the tool receptacle is again heated, and the opening is enlarged until the tool with its shaft can be withdrawn from the tool receptacle. The withdrawal is possible since the heating propagates from outside inwardly, so that first for example the sleeve part of the tool receptacle is heated up, before the heat reaches the shaft of the tool which is clamped in the receptacle. Thereby the sleeve portion is first expanded, so that the still cold shaft of the tool can be released during unchanging from the opening.
During the clamping of the shaft of the tool, the axial insertion depth of the shaft can be exactly adjusted in the opening of the tool receptacle, also with consideration of certain circumstances that during the subsequent cooling a length change will occur. It is known for clamping a tool, first to heat the tool receptacle until its opening is increased so that subsequently the tool with its shaft can be inserted into the opening. The insertion depth in the insertion is selected in correspondence with an assumption that an abutment which is integrated in the tool receptacle can be additionally provided. The insertion and the adjustment of the insertion depth are performed in heated condition of the tool receptacle with inwardly propagating terminal expansion of the inner receiving opening. This method operates only when during the short heating phase a sufficient time is available and when the tool is used with low thermal expansion, such as for example of hard metal or ceramic, since with these tool materials one must not be afraid that the heat supplied to the tool receptacle can be transferred to the tool shaft and cause its expansion and clamping during the insertion.
It is further known to adjust first an adjustment screw which is coaxially held in the tool receptacle, by means of an adaptor inserted in the opening of the tool receptacle in its cold condition, with respect to the axial nominal position. The adjustment can be performed by contacting or optical measurement, for example of the tip of the tool. After the complete adjustment of the coaxial adjustment screw and removal of the adaptor, the shrinking of the tool is performed by its shaft. During heating of the enlarged opening of the tool receptacle the tool can be inserted with its shaft so far until the end side of the shaft which is opposite to the tool tip axially abuts against the adjustment screw. The adjustment in this manner is not very accurate. Inaccuracies occur within the range of +/xe2x88x920.05 mm. This inaccuracy results from the fact that the tool, with respect to the above mentioned end side which reaches the contact with the adjusting screw, is not accurately treated. Also, the arrangement of the adjusting screw which is screwed in the central threaded opening coaxially to the opening is an additional expense, and also the thread pitch can cause additional adjustment errors.
Accordingly, it is an object of the present invention to provide a method of the above mentioned general type, which avoids the disadvantages of the prior art.
More particularly, it is an object of the present invention to provide a method of the above mentioned general type, which provides a very precise adjustment of the insertion depth of the tool with a simplified structural expenses of the tool receptacle.
It is also an object of present invention to provide a method of the above mentioned general type, which does not have any limitations with respect to the material pair tool receptacles/tool.
It is a further object of the present invention to provide a method of the above mentioned general type, in which not only tools with low thermal expansion can be utilized, such as hard metal, ceramic and the like, but also tools composed of other materials can be used as well.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated in a method of the above mentioned general type, in which with the tool coaxially supported relative the tool receptacle, for positioning of the tool a movable contact piece is arranged at its free end for abutment, and the tool is clamped between the contact piece at one side and a counterforce on the other side which acts on the tool in an opposite direction and opposite to an insertion into an opening of a tool receptacle before the heating starts, and during the heating it remains clamped, so that after reaching a predetermined nominal value during insertion of the shaft into the opening of the receptacle it is stopped.
In the inventive method the adjusting of the insertion depth of the tool shaft in the tool receptacle is performed before the heating of the tool receptacle. After the dimension reference, the relevant cutting geometry and not the end-side rear side of the tool shaft is utilized, and therefore a high quality exact adjustment is possible. With respect to the apparatus expenses, in particular the design of the tool receptacle, a simplification is provided because an inner adjusting screw with a threaded opening for receiving the same can be dispensed with and therefore the tool receptacle is simpler and less costly, and the danger of a pretensioning of mechanical parts is also eliminated. Before the heating of the tool receptacle, the movable contact piece is placed on the free end of the tool in abutment, so that the tool activates an oppositely directed, also coaxial, loading counterforce, and the tool can be held axially between the contact piece and the counterforce.
When the heating of the tool receptacle is performed with the opening of the tool receptacle increased due to the warning, the tool penetrates with its shaft into the larger opening of the tool receptacle. This insertion movement is performed because of the vertical arrangement under the action of the gravity forces. It can be also performed with the vertical arrangement and also with another spacial orientation of the arrangement manually and/or by driven means and/or by an adjustment drive, etc. The insertion of the tool clamped in the above mentioned manner, into the opening of the tool receptacle is stopped when the nominal value provided by adjustment is achieved. This stopping can be obtained by mechanical abutting against an abutment or in a similar way. When subsequently the heating is stopped, the tool receptacle is cooled and the tool shaft is clamped in a force-transmitting manner in the opening which is shrunk by cooling.
The method in accordance with the present invention is applicable equally for tools with low thermal expansion and for tools with high thermal expansion, so that both the tools of hard metal, ceramic and the like as well as tools composed for example of tool steel can be utilized. It should be taken into consideration that the heating phase is very short and as a rule is only approximately 5-10 seconds, and the adjustment of the tool together with a tool receptacle during insertion in the latter is performed during this short time period and simultaneously with the insertion in the opening of the tool receptacle, and so that it is not necessary to provide on the tool or the tool shaft mechanical clamping assisting means or the like.
In accordance with an advantageous embodiment of the present invention, the reaching of a predetermined nominal value is performed during insertion of the shaft in the opening by a mechanical abutment which is adjusted to a predetermined nominal value and is fixed, and is associated with the contact piece, in particular a movable holder of the contact piece. During insertion of the shaft into the opening the insertion path is limited by abutting against this abutment.
In accordance with another advantageous feature of present invention, the tool is brought with its shaft into an abutment opening of an abutment which is coaxially centered to a free end of the opening of the tool receptacle, in particular of the tool receptacle. The tool receptacle is located in not heated condition, the holder with its contact piece is placed on the tool, the counterforce acts on the tool opposite to the penetration into the opening of the tool receptacle, and thereby the clamping of the tool is activated between the contact piece and the counterforce. After this the heating of the tool receptacle starts with simultaneous axial insertion of the tool with the shaft into the opening of the tool receptacle so far until the holder abuts against the abutment. Thereafter the heating of the tool receptacle is stopped and after cooling the action of the counterforce is removed. The counterforce guarantees that the tool under the action of force of gravity is not introduced beyond the predetermined insertion depth into the opening of the tool receptacle. After cooling of the tool receptacle with the simultaneous shrinking of the opening and the clamping of the tool shaft, the action of the counterforce is eliminated.
It is also advantageous when the position of the contact piece which is placed on the tool, relative to the holder and in this way the position of the holder relative to the abutment is adjusted, preferably finely adjusted before the heating of the tool receptacle. For facilitating and reaching greater accuracy, an optical measuring system can be held on the holder with an acceleration device, a receiving device, an image screen with increased reproduction of the receiving region. Here by adjustment of the contact piece placed of the tool relative to the holder with the measuring system, an adjustment of the optical measuring system with optical scanning of a predetermined reference geometry of the tool is performed. For example, sensing of the tip of a drill, the highest cutting edge of a mill, the first or second stage of a stepped tool or a scanning of another dimension-determined edge of the tool are performed. By adjustment of the contact piece which is supported on the tip of the tool, the holder and thereby the optical system can be adjusted relative to the tool so that during further insertion of the tool in the opening of the tool receptacle the holder, by abutment against the abutment adjusted to the predetermined nominal value, limits the insertion depth of the tool from above, while a further deeper penetration of the tool in the opening is prevented by the counterforce which acts in an opposite direction. It is advantageous when the abutment is adjusted with respect to dimensional representation, for example a scale for adjustment of the nominal value, in particular for fine adjustment. Therefore in its adjusted position it is fixed relative to the dimensional representation, for example clamped, and in this position forms a mechanical abutment for the holder of the contact piece, or in some cases also the optical measuring system located on it.
It is also advantageous when during an axial insertion of this shaft of the tool in the opening of the tool receptacle, the nominal dimension is obtained, in particular during abutment of the holder against the abutment, and an electrical switch contact is closed so that the supply of electrical energy for heating of the tool receptacle is interpreted. This switch contact in a simple manner can be a component of the abutment and/or of the holder which contacts it, or is formed by it directly.
It is especially advantageous when at least the region of the contact piece which is brought into contact with the tool, for example its tip, edge, etc. is formed of such a material which is yieldable when compared with a material of the tool, for example softer. Such a material can be rubber, synthetic plastic or similar spring-elastic material, or instead a part of the contact piece can be biased by a spring. It is thereby guaranteed that during placement of the contact piece on the free end of the tool for example the tool piece, the tool which is sensitive in this situation is not damaged or is not negatively influenced in another way.
The counterforce which acts opposite to the insertion of the tool shaft in the opening can be produced, depending on the design of the tool and/or of the tool receptacle, in a mechanical manner, for example by an abutment, a gripper and the like, and transmitted to the tool. With such tools which are clamped with its whole shaft or are designed differently with respect to the geometry and with which it is not possible to engage mechanically or to act on them mechanically by the counterforce, it is especially advantageous when the counterforce is produced by a pressure gas cushion. It is advantageous to maintain the pressure gas cushion so long until, after ending the heating of the tool receptacle it is cooled during a subsequent holding time.
For producing the pressure gas cushion in the interior of the opening of the tool receptacle, it can be advantageous when in the opening of the tool receptacle, for example in the cooling medium passage provided in it, a pressure gas for example a pressure air is introduced. For loading such tool in the same way with a counterforce, which has inner cooling medium passages, it can be advantageous when for producing of the pressure gas cushion in this case a regulation of the volume stream of the pressure gas, for example by a throttling, is performed until required gas pressure is reached. It is further advantageous when the magnitude of the counterforce, in particular of the pressure gas cushion is adjusted so that it is equal or greater than the opposite gravity force of a tool received in the opening of the tool receptacle. Then with for example the electrical arrangement of the tool receptacle with the opening and the vertical penetrating shaft of the tool in the opening, the gravity force of the tool acts in the vertical direction. Before reaching of the predetermined nominal value and before reaching a corresponding adjusted abutment, on which during this vertical insertion movement the holder with the contact piece can act, additionally the gravity force of the tool, in particular the weight force of the holder partially acts. The sum of these weight forces, which however must but not required, can be taken by the counterforce, since after reaching the nominal value and thereby abutment of the holder against the abutment, the gravity force of the abutment is taken with the contact piece and the parts sitting on the holder before the abutment, and thereby the contact force is taken only by the gravity force of the tool.
It can be further advantageous when the magnitude of the counterforce is varied in correspondence having the tool with different geometry. For example for providing such an adjustment the weight of the corresponding tool can be determined by weighing in a weighing device, and the magnitude of the counterforce can be determined correspondingly and thereby applied. For example, in this way it can be realized that before the insertion of the tool in the supporting opening of the tool receptacle, first the weight of the tool receptacle and of the support of the same are determined. In a subsequent weighing process with the tool inserted in the abutment opening of the tool receptacle the weight of the above mentioned part together with the tool is determined by weighing and the difference provides a pure tool weight. Such an adaptation of the magnitude of the counterforce to different tool geometries is advantageous, when a predetermined value of the tool for the pressure gas cushion is not sufficient for all tool geometries.
It is further advantageous when the holder is moved with the contact piece by gravity force and/or manually and/or by driven means and/or by an adjustment drive. Thereby a movement which does not follow the gravity force is performed and has the advantage when the penetration of the shaft of the tool holder in the opening of the tool receptacle is performed not in a vertical direction, but instead in any direction which is transversed to it for example with horizontal arrangement and horizontal insertion of the tool. It is further advantageous when the movement of the holder is performed so that the contact piece performs a linear movement substantially coaxially or parallel to the longitudinal axis of the tool and/or transversely to it.
In accordance with a further embodiment of the method of the invention, the holder and the adjustable abutment are coupled with one another or are couplable with one another, so that during movement of the holder for example in both movement directions, the adjustment of the abutment can be performed. This has the advantage that the abutment does not need its own adjusting drive or the like, but instead a gravity force acting on the holder of the light means or adjustment drive without manual actuation is engaged. For example, a coupling between the holder and the abutment can be performed by a magnetic force in one direction so that, the abutment during movement of the holder in one direction is taken by a magnetic force, and during movement of the holder in the opposite direction can be taken by means of a form-locking contact, for example by abutment.
In accordance with another embodiment of the present invention, the tool with its shaft is insertable into a supporting opening of a support which is coaxially centered to a free end of a opening of a tool receptacle, and the tool receptacle is located in a not heated condition. Then a movable holder with a contact piece on an end of a tool is placed, and the position of the contact piece on the tool is adjusted preferably in a fine manner. Thereafter the opposite end of the tool is sensed with a measuring member opposite to the penetration of the tool into the opening of the tool receptacle, and this position of the measuring member is fixed.
This adjusting method has an advantage when it is not possible to load the lower end of the tool with a contact force, such as a pressure gas cushion. In this method first the holder with the contact piece and an upper abutment is moved until the contact piece contacts an end of a tool cutting edge provided on the tool. When this contact piece for example is composed of one micrometer is adjusted, the cutting edge of the tool is oriented in accordance with the thread cross of the optical measuring system, for example a profile projector. This optical measuring system, in accordance with the profile projector measures the height of the cutting edge of the tool. At the end the measuring member moves with its contact surface oppositely from below against the facing lower end side of the tool and senses the latter. This lower measuring member is adjusted in this manner and its function is controlled by a software.
Starting from the position of the optical measuring system, for example the profile projector, the software calculates the required adjusting path for the lower measuring signal to adjust the tool to the nominal value. Hereafter the lower measuring member is adjusted to its nominal position, whereby the end surface of the measuring member assumes the nominal abutment position for the associated lower end side of the tool. Then the tool is shrunk, and the tool is moved downwardly in the opening of the tool receptacle until its end side abuts against the facing end surface of the lower measuring member and thereby the axial nominal position is reached. Since the tool in these adjustment processes maintains its axial relative rotary position and the end surface which faces the lower end of the tool is not displaced, the adjustment of the lower measuring member leads to nominal abutment adjustment without errors.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.